The present invention generally relates to microelectronic assemblies, and more specifically it relates to semiconductor chip packages having light sensitive or light emitting chips.
The semiconductor chip packaging industry is a highly competitive business in which the packaging companies are waging an on-going battle to improve the reliability and cost of packaged chips. Moreover, the electronics industry continues to demand that chip packages take up less space within electronic components. As such, it is desirable that the overall size of the packaged chips be reduced so that the same circuitry fits into smaller areas thereby allowing for more portability (size, weight, etc.) for the resulting finished electronic product and/or allowing for an increase in a product's processing power without also increasing its size.
One type of semiconductor chip package includes packages which incorporate light sensitive semiconductor devices such as integrated circuits. When packaging such light sensitive devices (referred to herein as “IC's” or “chips”), it is necessary to allow for the passage of visible or near visible light, i.e. ultraviolet (“UV”) or infrared (“IR”) light, to the surface of the packaged chip. For example, ultraviolet-erasable programmable read-only memories (“UV EPROMS”) have traditionally been manufactured using a standard lead frame type package, as shown in FIG. 1. Typically in this type of package, a cavity is molded (as by an injection molding operation) around a lead frame and the back surface of the chip is attached to a paddle on the lead frame. The chip contacts on the face surface of the chip are then wire bonded to respective leads on the lead frame. This allows the chip assembly to be enclosed on three sides. The fourth side of the assembly is then fitted with a transparent lid made of glass or quartz so that the chip is physically protected but still capable of receiving light through the lid.
In a similar fashion, when packaging certain light emitting chips such as light emitting diodes (LED's), it is desirable to allow for the passage of visible or near visible light from a surface of the packaged chip. When manufacturing light emitting diodes, the LED's are commonly created on leadframe like structures. As shown in FIG. 2, an electrically conductive back surface of the chip is typically attached to an electrically conductive base on a first lead and chip contacts on a face surface of the chip are wire bonded to corresponding second leads. The base of the first lead typically has a notch within which the chip sits. The assembly is then encapsulated by using an injection molding technique. The encapsulant may form a lens on the top of the LED package to aid in the focusing of the light being emitted from the chip.
U.S. Pat. No. 4,890,383 to Lumbard et al. discloses another technique for packaging LED's which use a supporting frame or substrate as part of the package structure. As set forth in the '383 patent, the substrate comprises an electrically insulating material such as synthetic plastic. The top surface of the substrate includes a conductive pattern which defines a land area and a connection pad. A light emitting diode is mounted on the land area so that its terminal underneath is electrically and mechanically connected to the land area. The upper side of the light emitting diode is provided with a terminal which is electrically conductive and connected with the connection pad via a bonding wire.
A second conductive pattern of highly conductive material such as copper is deposited onto the rear surface of the substrate. This second conductive pattern defines a first terminal pad and a second terminal pad. The land area on the top side of the substrate is provided with an extension which is electrically connected to the terminal pad on the under side via a plated through groove having a semicircular cross-section. Similarly, the connection pad on the upper side of the substrate is provided with an extension which is electrically connected to the terminal pad on the under side via a plated through groove, which is preferably identical to the plated through groove. In this manner the two terminal pads serve as external terminals for the light emitting diode which mechanically secures modular component during surface mounting of the component. The assembly is provided with a transparent covering for protective purposes. Thus the light emitting diode and its electrical contacts including the bonding wire are sealed and encapsulated in the covering. The covering is made from clear or diffused epoxy, which provides optical characteristics.
Despite these and other efforts in the art, still further improvements in interconnection technology would be desirable. The chip packages manufactured in accordance with the prior art methods described above typically consume greater areas on a printed circuit board or within an electronic component than might otherwise be required. In addition, these particular prior art embodiments are also relatively complex and expensive.